Many fuel cells used in the production of electricity contain, sequentially, an electrolyte reservoir plate, an anode chamber, an anode electrode, an electrolyte, a cathode electrode, a cathode chamber, a second electrolyte reservoir plate, and a separator plate. Several of these fuel cells are aligned in electrical series to form a fuel cell stack capable of producing electricity.
During operation of the fuel cell stack, electric potentials are created across individual fuel cells and across the stack itself. These potentials are illustrated in FIG. 1 where the electric potential increases from the anode of cell 1 (A.sub.1) to the electrolyte at the anode of cell 1, decreases through the electrolyte of cell 1 (E.sub.1) between the anode and cathode, and then again increases to the cathode of cell 1 (C.sub.1). The potential then remains virtually constant from cell 1 to cell 2 across the cell 1 separator plate (S.sub.1) Then, again, cell 2's potential increases from the anode (A.sub.2) to the cathode (C.sub.2). This sequence continues through the fuel cell stack to the end cell. Even though, as can be seen at E.sub.1, E.sub.2, and E.sub.3, there is a slight decrease in potential across the electrolyte of each cell, the overall potential of an individual cell increases from the anode to the cathode. Similar electric potential differentials exist across the various fuel cell components during fuel cell shutdown.
Since high potentials, greater than about 0.9 volts (with respect to a hydrogen electrode), may cause electrode corrosion, while low potentials, less than about 0.1 volt, may damage the cathode catalyst, knowledge of these potentials can be utilized to limit or prevent corrosion and damage of the electrodes by establishing procedures to reduce the electric potentials thereof to a safe level. Therefore, what is needed in the art is a means for determining the electrochemical potential of the various fuel cell components.